The main goal of this proposal is to expand our understanding of the cognitive and neural deficits associated with Attention Deficit/Hyperactivity Disorder (ADHD) in the adult phenotype. The proposed experiment will use a cognitive neuroscience approach that combines specific behavioral tasks with simultaneous recording of event-related brain potentials (ERPs). All experiments will make comparisons of performance and brain activity patterns between ADHD subjects and controls matched for sex, age, and IG. We will investigate selective attention at three different processing levels: perceptual (Experiments 1 and 2), working memory (Experiments 3 and 4), and response selection and inhibition (Experiments 5 and 6). Conceiving of attention as a mechanism that selectively allocates processing resources according to cognitive load, we will try to determine in which of these processes selective attention is impaired in ADHD adults with respect to their control counterparts. In Experiment 1 subjects will be required to focus their attention selectively on a single sound source in a noisy acoustic environment. By recording ERPs to attended sounds and neighboring distracting sounds, we will determine whether ADHD subjects can focus their attention as sharply and accurately as the controls. Experiments will investigate the response to perceptual interference by measuring how well subjects can ignore irrelevant variations in one stimulus dimension while attending selectively to a second dimension. Experiment 3 will measure the capacity and temporal partners of visual working memory, while Experiment 4 will determine whether ADHD subjects can effectively respond to increasing processing demands being placed on visual working memory. Experiment 5 will record ERP measures of stimulus evaluation, response selection and error monitoring in a variant of the Eriksen flanker task. Experiment 6 will examine ERP indices of response inhibition in the stop-signal paradigm and will attempt to localize the underlying neural activity. In all these experiments, behavioral and electrophysiological measures will be compared and the anatomical sources of ERP components will be estimated in order to define the spatio-temporal patterns of cortical activity associated with normal and impaired attentional processes.